Fuel injectors (a.k.a. fuel nozzles) are important components of gas turbine engines. Because the fuel injector is the source of the fuel, the fuel injector can provide significant play in the role of engine performance.
Because the fuel injector is positioned, at least partially, within the engine case, a fuel injector includes a support/stem through which an internal fuel tube extends. The fuel tube will be connected to an atomizer or other tip member of the support/stem to improve the delivery state of the fuel so that it will more fully mix with air in the engine case. Typically, the fuel injector is positioned downstream of a compressor unit and upstream from a combustor of the turbine. Typically, the location between the compressor and the combustor in which, at least part of, if not a majority of, the fuel injector is located is referred to as a compressor discharge area.
During operation, the support/stem is surrounded by high-temperature and high-pressure compressor air. However, it is desirable to deliver the fuel at a much lower temperature than the high-temperature of the compressor air. More particularly, if too much heat is transferred to the fuel, the fuel can begin to coke, thereby ruining or reducing the quality of the fuel. Further, coking of the fuel can cause coke depositions in the fuel injector negatively effecting the fuel flow from the injector. The high heat also weakens the structural strength and exacerbates corrosion of the fuel nozzle.
As such, there have been many attempts to reduce the amount of heat that can be transferred from the high-temperature compressor air to fuel passing through the fuel injector. Typically, a heat shield is added that surrounds the stem/support providing a pocket of stagnant air around the support/stem to prevent or substantially reduce convection of heat to the support/stem.
Unfortunately, however, due to technology advances, thereby ever-increasing the harsh environment downstream of the compressor, the fuel injector is being exposed to and required to withstand higher environment temperatures, sometimes in excess of 1600 degrees Fahrenheit. Further, complicating the issue is the fact that fuel is being used more extensively as a heat sink or cooling agent for various systems, particularly in aircrafts, prior to consumption of the fuel. This is causing the fuel temperature as the fuel is being fed to the fuel injectors to rise sharply to 350 degrees Fahrenheit or higher, (i.e. prior to the fuel even entering the injector). Excessive temperature also weakens the strength and accelerates corrosion of the metal structures of the fuel nozzle. Typically, a fuel nozzle made of stainless steel losses strength noticeably at 800 degrees Fahrenheit and above, as does a fuel nozzle made of nickel alloy at 1200 degree Fahrenheit and above.
Due to these increases in temperature and sources of heat energy, standard heat shield/stagnant air arrangements are becoming less effective in preventing deleterious effects on the fuel.
The present invention relates to improvements over the current state of the art in fuel injectors.